1. Field of the Invention
This invention relates generally to earth boring, especially to improvements to bits having cutters rotatively secured to bearing shafts, with air passages through the interior of the bit and bearings to enable air or gas cooling of the bearings.
2. Background Information
Earth boring bits of the rolling cutter type consist of three general types: (1) Those having sealed bearings that are lubricated with a liquid lubricant confined in the bearing area, (2) those having open bearings where the fluid in the well bore is free to enter the bearings, and (3) the air or gas cooled, unsealed bit that has unsealed bearings cooled by the flow of fluid through passages in the body and the bearing of each leg.
Inevitably, it seems, there are some liquid and particles of dust or other debris pumped through the drill pipe supporting the bit. Often there is particle contaminated water on the bottom of the hole that flows backwardly into the bit when the air supply is stopped. All too frequently these ingredients form obstructions in one or more of the passages leading to the bearings, block the flow of cooling fluid and cause excessive heating and failure of one of the bearings.
Since the so called "air bit" is often used to drill repeatedly shallow holes in the mining industry, the accumulation of detritus in the passages of the bit is manually removed by the workers. This task is difficult since access to the internal air passages is limited, and may involve the removal from inside the shank of the screening tubes used over the cooling passages. Then, water is flushed through the passages, and a rod used to dislodge the blockage. These cleaning efforts are time consuming and difficult, partly because access to the passages is restricted.